This invention relates to a paper container for liquid and, more particularly, to a paper container for liquid sealed with gas in a head space formed in the top of the container after filling liquid therein, a method of filling the gas in the container and apparatus for filling the same gas.
A paper container for liquid is sealed by a packaging method to prevent bacteria or air from externally entering so as to increase the lifetime or shelf life of the contents in the same manner as a container such as a can or a bottle.
Particularly, juice drink, milk drink or coffee drink are known to be oxidized in the effective components by oxygen in the air, remarkably varied in taste or color, and corroded in the content by bacteria in the air deteriorating the value of merchandise in a short time.
Therefore, paper containers for the liquids are sealed from external atmosphere by packaging materials formed by laminating aluminum foil or synthetic resin film having low gas permeability on paper. Further, liquid heated for sterilization and then cooled is filled in a container sterilized to prevent the content from corroding to generally perform a so-called sterilization charging.
Moreover, immediately after the content liquid food is heated to 60 to 95.degree. C., the liquid is filled, sealed in the sterilized container to prevent bacteria from entering the container to normally perform a so-called packing method by hot filling. According to this method, air of the head space is evacuated out of the container by the vapor of the liquid food and the container is then sealed. Thus, the influence of the air to the content can be suppressed to some degree, but certain change of quality of the content liquid due to heat cannot be avoided.
In order to prevent the influence of the air in the head space of the container, the air in the head space is replaced by carbon dioxide gas or nitrogen gas in the container for filling solid content. However, when the carbon dioxide gas is used in a liquid food filling container, in many cases the gas is dissolved in the content to affect the taste of the food. Thus, this cannot be performed practically.
When the gas charge packing with nitrogen gas is applied to a paper container for liquid, it is naturally necessary to inspect the presence of gas substitution, the in pinholes of the container and the propriety of sealing of the container before delivering the container. Methods of inspecting the container include a method of removing and analyzing gas from a product, and a method of removing the content liquid by opening the container and inspecting it. In any of these methods, the inspected container cannot be recovered as merchandise, and the inspection takes a large quantity of time for no practical use. Therefore, there is no other way than a sampling inspection to test the reliability of the contents.